An Outdoor Guide to Scuba Diving
When divers use scuba sets as a way to dive underwater, it is referred to as scuba diving. Earlier diving relied on the diver holding their breath or on air being pumped from above the surface but now divers use their own breathing gas which is usually compressed air. This allows them to stay below the water much longer than they would be able to by simply holding their breath. Scuba divers usually move around under the water with swim fins that are attached to their feet. However, a propulsion vehicle for divers can be used as well.
Aqualung was the first scuba sets commercially available. This open-circuit, twin hose units were developed by Jacques-Yves Cousteau and Emile Gagnan and cylinders mounted on the back carried compressed air which the diver inhales through the demand regulator and exhaled into water next to the air tank. Today, two stage, single hose regulators are used. It separates the demand valve and the cylinder which gives the diver at his mouth rather than at the cylinder's top.
Normally, water contains dissolved oxygen which aquatic animals extract as water flows past their gills. Humans do not have gills and cannot breathe underwater without the use of external devices. It was quickly discovered that supplying air for breathing air comfortably was just not enough because pressure increases on the lungs and chest the deeper a diver goes down. This is why the pressure of air being inhaled must counter the ambient pressure to help inflate the diver's lungs. Demand valve regulators allow the diver to exhale and inhale without effort regardless of how deep underwater they go. The following links provide more information on what scuba divers use to breath underwater including open-circuit, closed-circuit, and semi-closed rebreathers as well as the gases used:
Divers need to be able to move while underwater. Dive gear that is streamlined helps reduce any drag and improve their mobility. Diver propulsion vehicles and swim fins help enhance personal mobility. For safe diving, divers have to control how fast they ascend and descend while in the water. Diving suits, buoyancy compensators, and diving suits are often used in order to help the diver's overall buoyancy.
The refractive index in water is higher than it is in air, similar to the eye's cornea. Light that enters the cornea is barely refracted which leaves the crystalline lens of the eye to focus the light. This leads to a severe case of hypermetropia. People who have severe myopia have the ability to see much better underwater without using a mask than the average person can. Helmets and diving masks help in solving the problem because they provide space for air in the front of the eye's of the diver. If a diver wears corrective lenses out of the water, they would need their same prescription when wearing a diving mask.
Red light is absorbed by water more than yellow and green. The color absorbed by water is blue. Because water is much denser than air, when light enters it, it interacts with the suspended particles and water molecules. This causes color change, light loss, diffusion, contrast, and various other effects. How light changes when you're underwater is due to the atmosphere underwater and there are many creative possibilities available that are not available on land which is a great opportunity for divers who are into underwater photography.
Because a diver cannot verbally communicate underwater without a mask fitting the entire face, they communicate by using various hand signals. For instance, when the diver raises their hand with their fingers up and palm facing the other diver, the same way a traffic officer signals you to stop, it means stop. When the diver extends their thumb down with their fist clenched, it means that they are going down or telling another diver to go down. If the diver extends both of their arms over their head touching their finger tips to make an O, it means OK. The receivers of the signal are to answer the signal by repeating the same signal sent.
A study done in North America in 1970 concluded that diving was more dangerous than driving a vehicle. The difference is that diver's are not at risk from other diver's whereas drivers are at risk from other drivers. Changes in pressure can cause injuries to divers and this is something they must avoid. Injuries due to pressure can be painful and possibly fatal causing ruptured lungs, eardrums, or sinus damage. Divers also pose risks from failing diving equipment, the environment they are diving in, and by not practicing or educating themselves enough on safety skills.